1. Field of Invention
This invention relates to wood pilings used for wharfs, piers or other marine structures, and particularly to systems for protecting the pilings from deterioration due to infestation and/or mechanical abrasion.
2. Discussion of the Prior Art
Marine borers have been the cause of great damage to marine pilings. Not uncommonly, creosote treated pilings have been branded unserviceable after six or seven years, particularly in warmer regions. The cause is a relatively new species of Limnoria that penetrates the wood, and then tunnels along the grain. Once the surface is penetrated, other marine borers, notably Toredo, mount a second wave attack.
A system for protecting marine piling from such marine animal destruction has been pioneered by Osmose, of Madison, Wis. This system, promoted under the trademark PILE-GARD, involves the use of thin flexible PVC plastic sheeting 0.030 inches thick, wrapped closely about the exterior of the piling from the mud line to above the intertidal zone. Seals create a closed envelope that soon stagnates to become permantely oxygen deficient. The entrapped borers die. Since none penetrates from the outside, the piling is thereby protected from further destruction and attack.
There are significant problems with the sheet plastic wrap system. Peripheral fender piles are exposed to impact by boats and floating debris. A partial solution is to nail vertical protective strips to the peripheral fender piles. The protective strips are themselves subject to abrasion; their fasteners deteriorate or loosen. Even interior piles are abraded by floating debris. All piles are subjects for vandalism. Polyvinyl chloride is not stable in the presence of creostote. Creosote embrittles the sheet material to the point where it ultimately cracks away. It has been proposed to utilize a second polyethylene sheet interposed between the creosoted pile and the other polyvinyl chloride sheet. The polyethlene sheet protects the outer sheet from cresote while the outer sheet protects the inner sheet from destructive ultra violet radiation.
A dual sheet arrangement still may require protective vertical bars or straps. Three elements must then be used for protection of a pile. Installation of a thin polyethylene sheet must be very carefully done. The polyethylene sheet is very easily ripped or torn. Elaborate surface preparation of the pile may be required. Even minor random folds in the polyethylene produce localized stress and ultimate rupture.